Flock-filled isocyanate-containing elastomer



June 19, 1956 F. s. MARTIN 2,751,363

FLOCK-F'ILLED ISOCYANATE-CONTAINING ELASTOMER Filed April 2, 1955 PA RTSFLO CK AI' I' OBNEY United States Patent O FLOCK-FILLED ISOCYANATE-CONTAININ G ELASTOMER Frank S. Martin, Cranston, R. I., assignor toUnited States Rubber Company, New York, N. Y., a corporation of NewJersey Application April 2, 1953, Serial No. 346,474 Claims. (Cl. 260-9)This invention relates to an improved composition of matter and moreparticularly to a cured mixture of an elastomeric synthetic polyurethanepolymer (by which is meant an elastomeric polymeric cross-linkedchainextended diisocyanate-modied polyester or polyester amide) and ock,this cured mixture having exceptionally high tear resistance.

Elastomeric synthetic polyurethane polymers have recently becomeimportant as new rubbery materials. Such elastomeric synthetic polymersare described in detail in an article by O. Bayer et al. which appearedin Rubber Chemistry and Technology, volume 23, pages 812-835 (1950). Asis now well-known, the elastomeric or rubbery synthetic polyurethanesare elastic materials capable when cured of being extended to more than200% and returning rapidly to approximately their original length andare made from three reactants, viz., (l) linear polyesters or polyesteramides, or mixtures thereof, (2) organic poly-isocyanates, and 3)initiators of cross-linking. The linear polyesters or polyester amidesemployed contain free hydroxyl or other groups containing activehydrogen such as free amino or amido groups.

These elastomeric synthetic polymers are often based upondiisocyanate-modied polyesters. As an example, adipic acid may bereacted with ethylene `glycol to produce a polyester with hydroxylgroups at each end of the polyester molecules. The individual polyestermolecules may be joined by reacting the terminal alcoholic hydroxylgroups with a diisocyanate such as p,pdiphenyl methane diisocyanate. Ifthe proper amount of the diisocyanate is used, the completed reactionwill leave terminal isocyanate groups on the polyester-diisocyanatereaction product. Subsequent reaction with wafer or the like inrelatively small amounts brings about urea bridging and thus introducesgroups which are capable of crosslinking by reacting with some of theunreacttd terminal isocyanate groups and converts the reaction productto the raw or gum state in which it resembles smoked sheet rubber. 'Ihenal cross-linking or vulcanizing reaction is brought about by heat in amanner which manipulatively closely resembles vulcanization of naturalrubber although chemically the cure is effected by a totally differentmechanism since the polyurethane polymer contains, built into itsmolecules as a result of the water reaction, everything required for itscuring which occurs as a result of reaction of the urea groups withremaining isocyanate groups.

In greater particularit many of the elastomeric synthetic polyurethanepolymers are made by (l) preparing a linear chain-extended polyesterfrom a glycol, for example, a mixture of ethylene and propylene glycols,and an aliphatic saturated dicarboxylic acid, for example, adipic acid,using an excess of the glycol over the acid so that the resulting linearpolyester contains terminal alcoholic hydroxyl groups, usually usingsuch an amount of glycol as to give the polyester a hydroxyl number of20 to 120 and preferably 40 to 80 and an acid value less than 2, (2)reacting this linear polyester with a diisocyanate, for example,naphthylene- LS-diisocyanate Aor vp,pdiphenyl methane diisocyanate,using a considerable excess, commonly from 20 to 250% and preferablyfrom 50 to 100%, of the diisocyanate over the theoretical amountcorresponding to the alcoholic hydroxyl groups furnished by thepolyester, by heating a mixture of the polyester and the diisocyanateunder anhydrous conditions at an elevated temperature, e. g., -150 C.,to form a liquid material which is a linear polyurethane having terminalisocyanate groups, and (3) reacting this liquid material (which is oftentermed a "polyester-diisocyanate) with a small amount of Water,typically equal to about 0.6 to 0.95 mol per mol of the liquid materialto convert the liquid material to solid (gum) form resembling uncured(gum) smoked sheet natural rubber. The water reacts with a portion onlyof the isocyanate groups present, converting them to -NHz groups whichare highly reactive withother isocyanate groups to form urea groupswhich are reactive with remaining isocyanate groups to give a highlycross-linked product. The gum material is cured, i. e., is converted toa form resembling vulcanized natural rubber by simply heating it underpressure at an elevated temperature, say 10Q-170 C., for a suitableperiod of time, say from l0 minutes to two hours. Instead o' water asthe material used to convert the liquid intermediate to gum form andinitiate the curing mechanism, other chemicals, e. g., trihydric andhigher polyhydric alcohols, beta-aminoethyl alcohol, and polyamines suchas diamines, can be used.

Other commercially important synthetic elastomeric polyurethane polymersare made in the same way except that the polyester is replaced with apolyester amide, such as one made by esten'fying a glycol with analiphatic saturated dicarboxylic acid in the presence of an aminoalcohol, e. g., an alkanolamine, or a diamine, e. g., an alkylenediamine.

In some cases the synthetic elastomeric polyurethane polymer is made byreacting together in suitable fashion (l) a polyester or polyesteramide, (2) a bifunctional compound like a diamine, and (3) adiisocyanate, such as naphthylene-l,S-diisocyanate or p,pdiphenylmethanediisocyanate to give an uncured elastomeric product, and etfectingcuring of the resulting uncured reaction product by intimately admixing-therewith an organic polyisocy-` anate, generally a diisocyanateidentical with that previously employed, in amount sufficient to electcurring, often in amount such as to bring the total number of NCOequivalents in the cured composition to around 3 equivalents of NCO permol of polyester or polyester amide, and subjecting the resultingmixture to heat and pressure.

The Vcured elastomeric synthetic polyurethane polymers have many of thephysical characteristics of natural rubber and similar elastomericmaterials. They have good abrasion-resistance and tear-resistance andthese properties make them considerably better than natural rubber orthe more common synthetic rubbers for many uses. However, the tearresistance of these synthetic polyurethane polymers is not sutlcientlyhigh for many purposes.

The principal object of theV present invention is to greatly enhance thealready high tear-resistance of such elastomeric synthetic polyurethanepolymers and to render them highly suitable for use in applicationsrequiring exceedingly high tear-resistance, for example, in thefabrication of articles made by sewing relatively thin sheets of thepolymers to form clothing, bags, cases, covers, and

p the like.

I have discovered that the addition of flock to the elastomericsynthetic polyurethane polymer prior to curing thereof brings about aremarkable increase in its tear resistance. This was highly unexpectedbecause flock does not materially increase the tear resistance ofordinary rubber. The Acurves in the accompanying drawing com-`V pare thebehavior of flock as a filling agent in rubber (by which is meantnatural rubber) with its behavior 'n synthetic elastomeric polyurethanepolymers. It should be pointed out that the curves in the drawingaccurately portray general trends observed in a number of experimentsand do not reproduce exactly the results of any given series ofexperiments. The incorporation of flock with natural rubber inincreasing amounts follows the characteristic pattern shown by thecurves labelled Rubber in Figs. 1, 2 and 3. These curves show that asthe amount of flock is increased the tensile strength and elongationdecrease while the tear resistance increases only slightly. Essentiallyidentical results are obtained with different types of flock, e. g.,cotton, nylon and rayon flock. The composition of the natural rubbercompound from which the curves labelled Rubber were obtained was asfollows:

NATURAL RUBBER-FLOCK COMPOUND Parts by weight Smoked sheets naturalrubber -100 Stearic acid 1 Zinc oxide Mercaptobenzothiazole(accelerator) 1 Sulfur 3 Flock As indicated The above compound was mixedon an open rubber mill and press cured in slab form in the mannerconventionally used in studying rubber compounds. The cures were for l5and 30 minutes with steam at a pressure of 40 pounds per square inch inthe press platens (141 C.). Tensile, elongation and tear values weremeasured on the conventional Scott tester. Tear-resistance was measuredwith the grain of the sample using the rectilinear tear test and asample 0.10 inch thick. The natural rubber curves, showing the effect ofincreasing the flock content of the rubber compound, followed theexpected pattern.

Unexpected results were obtained when synthetic elastomeric polyurethanepolymer compounds were made and cured in order to determine the effectof adding varying proportions of flock to such a polymer. Typicalresults are portrayed by the curves designated isocyanate-PolyesterRubber in Figs. l, 2 and 3, the physical properties being measured inthe same way as for the regular rubber compounds and being shown asfunctions of the parts of flock added per 100 parts of syntheticelastomeric polyurethane polymer. Figs. 1 and 2 show the data forvcottonflock. Examination of Fig. 1 shows that the tensile follows about thepattern in natural rubber, although it is higher and there is someindication that it may go through ak minimum at some value between 2Gand 40 parts of flock and then increase with the addition of more flock.Examination of Figs. 2 and 3 shows that the elongation and particularlythe tear-resistance curves are very unusual. As the amount of flock isincreased above about parts the elongation suddenly drops to a low valueand continues to decrease at a slower rate as more flock is added. Atabout the same point at which the elongation suddenly decreases, thetearresistance goes through a very pronounced maximum.

The maximum tear-resistance obtained by adding in creasing amounts offlock is three to five times that obtained with the uncompoundedsynthetic polyurethane polymer. The amount of flock required to producethe maximum tear-resistance and the maximum tear-resistance obtainedvary with the type of flock used.

The cotton and nylon flocks gave roughly the same tear-resistance whilethe rayon flock gave substantially higher tear-resistance than eithercotton or nylon flock. The size of fibers in the flock may be of someimportance in determining the actual values of the maximumtearresistance obtained with any specific type of flock. However, allofthe flocks tested gave unexpectedly high tearresi'stance at avaluebetween 101 and SO-partst of flock per 100,'` parts` of; synthetic;polyurethane polymer.

The isocyanate-polyester rubber compound used was as follows:

ISOCYANATE-POLYESTER RUBBER-FLOCK as follows: Adipic acid is esterifiedwith an excess ure of ethylene and propylcne glycols in a molar ratio esof ethylene glycol to 30 moles of propylene glycol,

of TO in water boing distilled off followed by a removal of some glycolby distillation to give a polyester containing terminal alcoholichydroxyl groups. This polyester has a hydroxyl value of about 50, anacid value below 2 and a molecular weight of about 2,000. This polyesteris then reacted with p,pdiphenyl methane diisocyanate, using two molesof the latter per mole of the former to give a liquidpolyesterdiisocyanate intermediate. This liquid intermediate is placedin a Werner- Pfliederer mixer and water in amount equal to about 1 moleper mole of intermediate is added with mixing to convert the liquidintermediate to the uncured gum stage.

The isocyanate-polyester rubber-flock compound was prepared for testingby mixing the uncured rubbery isocyanate-polyester-water reactionproduct with the flock on a rubber mill, sheeting out, and curing thesheeted mixture in a press in a manner similar to that conventionallyused for the preparation of test slabs of ordinary rubber compounds.Mixing was carried out on a cold rubber mill and curing was for 30minutes with steam at a pressure of 40 p. s. i. in the press platens.

While I prefer to use from l0 to 30 parts of the flock per parts ofpolyurethane polymer, I can use a somewhat broader range, say from 2 to40 parts per 100 parts of polymer.

Instead of mixing the flock with the uncured gum polyurethane, asdescribed above, l can use other methods of preparing the flock-filledcompositions contemplated by my invention. For example, l can intimatelyincorporate the flock with the polyester-diisocyanate intermediate priorto reaction thereof with water or other chemical to introduce the ureabridging groups and initiate the curing reaction. This intermediate isusually a liquid resembling molasses in consistency and, like molasses,becoming less viscous when warmed. However, it may be a solid, which isthermoplastic, being linear. The extremely high chemical reactivity ofthe intermediate makes it very practical to incorporate the flockdirectly therewith, since this provides an opportunity for chemicalreaction between the intermediate and the flock. Such reaction isexpedited if the intermediate is in liquid condition when the flock isincorporated therewith.

I believe that the unique results of my invention are due to chemicalreaction between the flock and the polyesterdiisocyanate intermediate orthe uncured gum material produced therefrom. Thus those flocks which aremade from cellulose, e. g., cotton or rayon flock, contain hydroxylgroups, While nylon flock, being a synthetic linear polyamide, containsreactive groups. Glass flock contains water molecularly adsorbed on itssurface and also contains other reactive groups on its surface.

As will be obvious, in practicing my invention I incorporate the flockwith either the polyester-diisocyanate reaction product or the uncuredgum rubbery material produced by reacting this reaction product withWater 0r the like. Those skilled in the art can readily distinguish thisuncured rubbery material from the cured material by the fact that theuncured material can be milled on a rubber mill in a manner similar touncured natural rubber whereas the cured material has undergone achemical cross-linking reaction which converts it to a state such thatit cannot be milled in this manner.

The following examples illustrate my invention in more detail.

Natural rubber compounds and synthetic polyurethane elastomer compounds,filled with varying amounts of cotton flock, rayon flock and nylon flockwere prepared accordingV to the above formulations, sheetedl out, curedin the manner described above and tested with the results shown inTables I to VI below.

The cotton flock used in these stocks was that known as F60 supplied byHarwick Standard Chemical Co., Boston, Mass. The rayon tlock was thatknown as F-7 Verlon Flock and the nylon flock was that known as N706Nylon Flock, both supplied by Vertipile Cornpany, Lowell, Mass.

Table I COTTON FLOOK LOADING OF NATURAL RUBBER Parts of Hoek per 100rubber 2 5 10 20 30 50 Tensile, p. s.i 3, 500 3, 000 2,500 2,200 1,8001, 400 800 Elongation, percent.- 800 775 750 725 650 550 450 Tear 7.58.0 7.3 8.0 11. 13 11 Table Il RAYON FLOCK LOADING OF NATURAL RUBBERParts of ock per 100 rubber 0 2 5 10 20 30 50 Tensile, p. s. i. 3, 5003, 000 2, 100 2, 000 1, 700 1, 300 850 Elongation, percent.- 800 775 725700 650 575 500 Tear 7. 5 6. 5 6. 3 7.0 9. 7 11 17 Table III NYLON FLOCKLOADING OF NATURAL RUBBER Parts of ock per 100 rubber 0 2 5 10 20Tensile, p. s.i 3, 500 3, 000 2, 700 2, 400 l, 600 Elongation, percent800 750 750 700 650 Tear 7.5 6.3 6.3 7. 3 8.0

Table IV COTTON FLOCK LOADING OF ISOCYANATE- POLYESTER RUBBER Parts offlock per 100 rubber 0 10 15 20 30 50 Tensile, p. s.i 2, 650 2, 150 l,700 2, 300 2, 800 Elongation,percent. 650 600 150 50 25 Tear 13 38 44 3823 14 Table V RAYON FLOCK LOADING OF ISOOYANATETOLYESTER RUBBERPartsofflockperlorubber 5 10 I 15 20 30 I 50 Tensile, p. s. i 5, 000 3,200 3, 100 2,100 2, 200 2, 600 Elongation, percent 700 700 650 500 50 25Tear 35 56 69 78 75 16 Table VI NYLON FLOGK LOADING OFISOCYANATE-POLYESTER RUBBER PartsoftlockperlOOrubber 5 10 15 20 30 l 506 Rubber Age, N. Y. 6l, 697-703 (1947)) or it may be monolamentary as inthe case of rayon or nylon or glass Hock which is made from artiiiciallyformed monoiiliamentary material. I can use ilocks other than thosementioned above, e. g., wool ock.

As an example of the use of glass ock in my invention, I compoundedparts of the uncured isocyanatepolyester rubber used in the aboveexamples with 15 parts of the glass ock known as Fibra Glass (choppedglass ber having a cationic sizing, furnished by Owens- Corning FiberGlass Co. of Newark, Ohio) and cured in the same way as before. Thecured samples had the following physical properties:

The invention can be used for making any form of article. It isparticularly useful for making improved articles requiring an airandWater-impervious rubbery sheet such as a thin unsupported sheet ofrubbery material or a sheet of fabric which has been proofed on one orboth sides with a thin layer of the rubbery material of the invention.Sheeting embodying flock-reinforced rubbery material made in accordancewith the invention can advantageously be used in place of iilms orcoated fabrics used in making Waterproof clothing, diaphragms,upholstery material, luggage covering, equipment covers, instrumentbags, carrying cases and the like. Thin sheets, with or without fabricreinforcement, can readily be sewn in the manufacture of articles of thetypes just mentioned. The seams of such articles show no tendency tofail because of tearing of the elastomeric sheet at the stitches as isthe case with such articles made from unsupported sheets of ordinaryrubber or of plastic.

The flock-reinforced elastomeric material of my invention can be usedadvantageously in applications requiring high tear-resistance in arubbery material, in either sheet or solid form. The ock-reinforcedmaterial of my invention can be used to replace leather in many articlessuch as belts, shoes, bags, cases, covers, bellows, ball covers, etc.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

1. A synthetic elastomeric composition characterized by improved tearresistance comprising from 2 to 40 parts of a brous liock selected fromthe group consisting of cellulose flock, nylon flock, glass flock andwool ock as a reinforcing filler for the said elastomeric composition,and 100 parts of a polyurethane polymer which is a reaction product of apolyester and a diisocyanate cured to an elastomeric state in thepresence of available isocyanate groups attached to the saidpolyurethane, and said polymer having been cured in admixture with thesaid flock.

2. A synthetic elastomeric composition characterized by improved tearresistance comprising (A) 100 parts of polyurethane polymer which is areaction product of a polyester and a diisocyanate and which containsterminal isocyanate groups, cured to an elastomeric state in admixturewith (B) from 10 to 30 parts of cellulose ock, as a reinforcing tillerfor the said elastomeric composition.

3. A synthetic elastomeric composition as in claim 2 in which the saidcellulose ock is cotton ock.

4. A synthetic elastomeric composition characterized by improved tearresistance comprising (A) 100 parts of a polyurethane polymer which is areaction product of a polyester and a diisocyanate and which containsterminal isocyanate groups, c'ured to an elastomeric state in admixturewith (B) from l0 to 30 parts of nylon flock, as a reinforcing filler forthe said elastomeric composition.

5. A synthetic eiastomeric composition characterized References Cited inthe ie of this patent by improved tear resistance comprising (A) 100parts y UNITED STATES PATENTS of a polyurethane polymer which is areaction product of a polyester and a diisocyanate and which contains2490001 Jayne etal n Nov 29' 1949 terminal isocyanate groups, cured toan elastomeric state 5 OTHER REFERENCES in admixture with (B) from 10 to30 parts of glass ock, Bayeret al Article` in Rubber Chem & Tech Oct, asa reinforcing ller for the said elastomeric composi- Decw 1950,"pages814 820 823 824, 26 and 21 tion.

1. A SYNTHETIC ELASTOMERIC COMPOSITION CHARACTERIZED BY IMPROVED TEARRESISTANCE COMPRISING FROM 2 TO 40 PARTS OF A FIBROUS FLOCK SELECTEDFROM THE GROUP CONSISTING OF CELLULOSE FLOCK, NYLON FLOCK, GLASS FLOCKAND WOOL FLOCK AS A REINFORCING FILLER FOR THE SAID ELASTOMERICCOMPOSITION, AND 100 PARTS OF A POLYURETHANE POLYMER WHICH IS A REACTIONPRODUCT OF A POLYESTER AND A DIISOCYANATE CURED TO AN ELASTOMERIC STATEIN THE PRESENCE OF AVAILABLE ISOCYANATE GROUP ATTACHED TO THE SAIDPOLYURETHANE, AND SAID POLYMER HAVING BEEN CURED IN ADMIXTURE WITH THESAID FLOCK.